4

Configuring Load Balancing Pools

Introducing load balancing pools

In a typical client-server scenario, a client request goes to the destination IP address specified in the header of the request. For sites with a large amount of incoming traffic, the destination server can quickly become overloaded as it tries to service a large number of requests. To solve this problem, the BIG-IP®local traffic management (LTM) system distributes client requests to multiple servers instead of to the specified destination IP address only. You configure the LTM system to do this when you create a load balancing pool.

What is a load balancing pool?

A load balancing pool is a set of devices, such as web servers, that you group together to receive and process traffic. Instead of sending client traffic to the destination IP address specified in the client request, the LTM system sends the request to any of the servers that are members of that pool.

When you create a pool, you assign servers (known as pool members) to the pool, and then associate the pool with a virtual server in the LTM system. The LTM system then directs traffic coming into the virtual server to a member of that pool. An individual server can belong to one or multiple pools, depending on how you want to manage your network traffic.

The specific pool member to which the LTM system chooses to send the request is determined by the load balancing method that you have assigned to that pool. A load balancing method is an algorithm that the LTM system uses to select a pool member for processing a request. For example, the default load balancing method is Round Robin, which causes the LTM system to send each incoming request to the next available member of the pool, thereby distributing requests evenly across the servers in the pool. For a complete list of load balancing methods, see Specifying the load balancing method.

Features of a load balancing pool

You can configure the LTM system to perform a number of different operations for a pool. You can:

Associate health monitors with pools and pool members

Enable or disable SNAT connections

Rebind a connection to a different pool member if the originally-targeted pool member becomes unavailable

Set the Quality of Service or Type of Service level within a packet

Specify a load balancing algorithm for a pool

Assign pool members to priority groups within a pool

Creating and modifying load balancing pools

You use the Configuration utility to create a load balancing pool, or to modify a pool and its members. When you create a pool, the LTM system automatically assigns a group of default settings to that pool and its members. You can retain these default settings or modify them. Also, you can modify the settings at a later time, after you have created the pool.

It is helpful to understand that the LTM system designates some settings as basic and others as advanced. If you decide to modify some of the default settings when you create the pool, be sure to select the Advanced option on the screen to view all configurable settings. For more information on basic and advanced settings in general, see Chapter 1, Introducing Local Traffic Management.

Creating and implementing a load balancing pool

Creating and implementing a load balancing pool is a two-task process:

First, you must create the pool.

Second, you must associate the pool with a virtual server.

To create a load balancing pool

On the Main tab, expand Local Traffic.

Click Pools.The Pools screen opens.

In the upper-right corner of the screen, click Create.The New Pool screen opens.

From the Configuration list, select Advanced.

For the Name setting, type a name for the pool.

Specify, retain, or change each of the other settings.For information on pool settings, see Configuring pool settings, or refer to the online help for this screen.

To implement a load balancing pool

Click the name of the appropriate virtual server.This displays the settings for that virtual server.

On the menu bar, click Resources.

In the Default Pool list, select the name of your newly-created pool.

Click Update.

Modifying a load balancing pool

You can modify any settings configured for an existing pool, including the load balancing method. For information on pool settings, see Configuring pool settings, or see the online help. For information on adding members to an existing pool, see Modifying pool membership, following.

To modify pool settings

On the Main tab, expand Local Traffic.

Click Pools.The Pools screen opens.

Click the name of an existing pool.This displays the existing settings for that pool.

From the Configuration list, select Advanced.This displays the pool settings.

Modify or retain all settings.

Click Update.

If you want to modify the load balancing method or enable or disable priority group activation, locate the menu bar and click Members.

Modify or retain the Load Balancing Method and Priority Group Activation settings.

Click Update.

Modifying pool membership

For an existing load balancing pool, you can either modify existing pool members or add new members to the pool.

Modifying existing pool members

When modifying settings for members of a pool, you can:

Enable or disable pool members

Remove members from the pool

Modify the values of pool member settings

To modify existing pool members

On the Main tab, expand Local Traffic.

Click Pools.The Pools screen opens.

In the Members column, click the number shown.This lists the existing members of the pool.

Locate the Current Members section of the screen.

Modify a pool member:

If you want to enable or disable a pool member, or remove a member from the pool, click the box to the left of a member address. Then click Enable, Disable, or Remove.

If you want to modify the settings for a pool member, click an address and retain or modify pool member settings as needed. For information on pool member settings, see Configuring pool member settings.

Click Update.

Adding members to an existing load balancing pool

Not only can you specify pool members at the time that you create a pool, you can add pool members later on. When adding a pool member to an existing pool (as opposed to specifying a pool member during pool creation), you can configure a number of settings for that pool member. The only settings that you must explicitly specify are the Address and Service Port settings. All other settings have default values that you can either retain or adjust, depending on your needs.

NoteIf you specify a pool member at the time that you create a pool, you do not see these settings; instead, the LTM system simply assigns default values. However, you can adjust the settings later by modifying the pool member properties. For more information, see Managing pools and pool members.

To add members to a load balancing pool

On the Main tab, expand Local Traffic.

Click Pools.The Pools screen opens.

In the Members column, click the number shown.This lists the existing members of the pool.

In the right side of the screen, click Add.The New Pool Members screen opens.

In the Address box, select New Address and type an IP address, or select Node List and select an IP address.

In the Service Port box, type a port number or select a service from the list.

Configuring pool settings

You can configure pool settings to tailor pools to your specific needs. For those settings that have default values, you can retain those default settings or modify them. Also, you can modify any settings either when you create the pool, or at any time after you have created it. For information on how to use the Configuration utility to configure these settings, see Creating and modifying load balancing pools.

Table 4.1 lists the settings that you can configure for a pool, followed by a description of each setting.

Table 4.1 Settings for a load balancing pool

Pool Setting

Description

Default Value

Name

You can specify the user-supplied name of the pool. Specifying a name for a pool is required.

No default value

Health Monitors

You can associate a health or performance monitor with an entire pool, rather than with individual pool members only. This eases the task of configuring health and performance monitoring for multiple web servers.

No default value

Availability Requirement

You can specify the number of monitors that must report a pool member as being available before that member is defined as being in an up state.

All

Allow SNAT

You can configure a pool so that SNATs are automatically enabled or disabled for any connections using that pool.

Yes

Allow NAT

You can configure a pool so that NATs are automatically enabled or disabled for any connections using that pool.

Yes

Action on Service Down

If this setting is enabled and the target pool member goes down, the LTM system tries to choose another pool member and rebind the client connection to a new server connection. Possible values are None, Reject, Drop, and Reselect.

None

Slow Ramp Time

This option causes the BIG-IP system to send a less-than-normal amount of traffic to a newly-enabled pool member for the specified amount of time.

0

Link QoS

You can configure a pool to set a specific Quality of Service (QoS) level within a packet, based on the targeted pool.

0

IP ToS

You can configure a pool to set a specific Type of Service (ToS) level within a packet, based on the targeted pool.

0

Load Balancing Method

You can use the default load balancing method, or you can define another load balancing method, and you can configure priority-based member activation. Different pools can be configured with different load balancing methods.

Round Robin

Priority Group Activation

You can assign pool members to priority groups within the pool.

Disabled

New Members

For each pool that you create, you must specify the servers that are to be members of that pool. Pool members must be specified by their IP addresses. For each pool member, you can also assign a service port, a ratio weight, and a priority group.

No default value

Before configuring a pool, it is helpful to have a description of certain pool settings that you might want to change.

Specifying a pool name

The most basic setting you can configure for a pool is the pool name. Pool names are case-sensitive and may contain letters, numbers, and underscores (_) only. Reserved keywords are not allowed.

Each pool that you define must have a unique name.

Associating health monitors with a pool

Monitors are a key feature of the LTM system. Monitors help to ensure that a server is in an up state and able to receive traffic. When you want to associate a monitor with an entire pool of servers, you do not need to explicitly associate that monitor with each individual server. Instead, you can simply use the pool setting Health Monitors to assign the monitor to the pool itself. The LTM system then automatically monitors each member of the pool.

The LTM system contains many different pre-configured monitors that you can associate with pools, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with pools. The only monitor types that are not available for associating with pools are monitors that are specifically designed to monitor nodes and not pools or pool members. These monitor types are:

ICMP

TCP Echo

Real Server

SNMP DCA

SNMP DCA Base

WMI

With the LTM system, you can configure your monitor associations in many useful ways:

You can associate a monitor with an entire pool instead of an individual server. In this case, the LTM system automatically associates that monitor with all pool members, including those that you add later. Similarly, when you remove a member from a pool, the LTM system no longer monitors that server.

When a server that is designated as a pool member allows multiple processes to exist on the same IP address and port, you can check the health or status of each process. To do this, you can add the server to multiple pools, and then within each pool, associate a monitor with the that server. The monitor you associate with each server checks the health or performance of the process running on that server.

When associating a monitor with an entire pool, you can exclude an individual pool member from being associated with that monitor. In this case, you can associate a different monitor for that particular pool member, or you can exclude that pool member from health monitoring altogether. For example, you can associate pool members A, B, and D with the http monitor, while you associate pool member C with the https monitor.

You can associate multiple monitors with the same pool. For instance, you can associate both the http and https monitors with the same pool.

Specifying the availability requirements

This setting specifies a minimum number of health monitors. Before the LTM system can report the pool member as being in an up state, this number of monitors, at a minimum, must report a pool member as being available to receive traffic.

To configure this setting, type a number in the Availability Requirement box.

Allowing SNATs and NATs

When configuring a pool, you can specifically disable any secure network address translations (SNATs) or network address translations (NATs) for any connections that use that pool. You do this by configuring the Allow SNAT and Allow NAT settings. By default, these settings are enabled. You can change this setting on an existing pool by displaying the Properties screen for that pool.

One case in which you might want to configure a pool to disable SNAT or NAT connections is when you want the pool to disable SNAT or NAT connections for a specific service. In this case, you could create a separate pool to handle all connections for that service, and then disable the SNAT or NAT for that pool.

Specifying action when a service becomes unavailable

The Action on Service Down setting specifies the action that you want the LTM system to take when the service on a pool member becomes unavailable. The possible settings are:

None -- The LTM takes no action. This is the default action.

Reject -- The LTM system sends an RST or ICMP message.

Drop -- The LTM system simply cleans up the connection.

Reselect -- The LTM system selects a different node.

To configure this setting, locate the Action on Service Down setting and select a value from the list.

Configuring a slow ramp time

When you take a pool member offline, and then bring it back online, the pool member can become overloaded with connection requests, depending on the load balancing mode for the pool. For example, if you use the Least Connections load balancing mode, the system sends all new connections to the newly-enabled pool member (because technically, that member has the least amount of connections).

When you configure the Slow Ramp Time setting, the system sends less traffic to the newly-enabled pool member. The amount of traffic is based on the ratio of how long the pool member has been available compared to the slow ramp time, in seconds. Once the pool member has been online for a time greater than the slow ramp time, the pool member receives a full proportion of the incoming traffic.

To configure this setting, locate the Slow Ramp Time setting and type a number.

Configuring the Quality of Service (QoS) level

Another setting of a pool is the Quality of Service (QoS) level. The QoS level is a means by which network equipment can identify and treat traffic differently based on an identifier. Essentially, the QoS level specified in a packet enforces a throughput policy for that packet.

As traffic enters the site, the LTM system can set the QoS level on a packet, based on the QoS level that you define for the pool to which the packet is sent. The LTM system can also apply an iRule that sends the traffic to different pools of servers based on the Quality of Service level.

The LTM system can tag outbound traffic (the return packets based on an HTTP GET) based on the QoS value set in the pool. That value is then inspected by upstream devices and given appropriate priority. Based on an iRule, the LTM system can examine incoming traffic to see if it has a particular QoS or ToS tag in the header. The LTM system can then make an iRule-informed load balancing decision based on that tag.

For example, to configure a pool so that a QoS level is set for a packet sent to that pool, you can set the Client level to 3 and the Server level to 4. In this case, the QoS level is set to 3 when sending packets to the client and the QoS level is set to 4 when sending packets to the server.

In addition to configuring a pool to set the QoS level on a packet, you can configure an iRule that selects a pool based on the existing QoS value within the packet. For more information, see Chapter 13, Writing iRules.

Configuring the Type of Service (ToS) level

Another pool setting is the Type of Service (ToS) level. In addition to the QoS level, the ToS level is another means by which network equipment can identify and treat traffic differently based on an identifier. As traffic enters the site, the LTM system can set the ToS level on a packet, based on the ToS level that you define for the pool to which the packet is sent. The LTM system can also apply an iRule and send the traffic to different pools of servers based on the ToS level.

The LTM system can tag outbound traffic (the return packets based on an HTTP GET) based on the ToS value set in the pool. That value is then inspected by upstream devices and given appropriate priority. Based on an iRule, the LTM system can examine incoming traffic to see if it has a particular ToS tag in the header. The LTM system can then make an iRule-informed load balancing decision based on that tag.

For example, to configure a pool so that a ToS level is set for a packet sent to that pool, you can set both the Client level and the Server level to 16. In this case, the ToS level is set to 16 when sending packets to the client and the ToS level is set to 16 when sending packets to the server.

NoteIf you change the ToS level on a pool for a client or a server, existing connections continue to use the previous setting.

In addition to configuring a pool that sets the ToS level on a packet, you can configure an iRule that selects a pool based on the existing ToS value within the packet. For more information, see Chapter 13, Writing iRules.

Specifying the load balancing method

Load balancing is an integral part of the LTM system. Configuring load balancing on an LTM system means determining your load balancing scenario, that is, which pool member should receive a connection hosted by a particular virtual server. Once you have decided on a load balancing scenario, you can specify the appropriate load balancing method for that scenario.

A load balancing method is an algorithm or formula that the LTM system uses to determine the node to which traffic will be sent. Individual load balancing methods take into account one or more dynamic factors, such as current connection count. Because each application of the LTM system is unique, and node performance depends on a number of different factors, we recommend that you experiment with different load balancing methods, and select the one that offers the best performance in your particular environment.

Using the default load balancing method

The default load balancing method for the LTM system is Round Robin, which simply passes each new connection request to the next server in line. All other load balancing methods take server capacity and/or status into consideration.

If the equipment that you are load balancing is roughly equal in processing speed and memory, Round Robin mode works well in most configurations. If you want to use the Round Robin method, you can skip the remainder of this section, and begin configuring other pool settings that you want to add to the basic pool configuration.

Selecting a load balancing method

If you are working with servers that differ significantly in processing speed and memory, you may want to switch to one of the Ratio or dynamic methods.

Round RobinThis is the default load balancing method. Round Robin mode passes each new connection request to the next server in line, eventually distributing connections evenly across the array of machines being load balanced. Round Robin mode works well in most configurations, especially if the equipment that you are load balancing is roughly equal in processing speed and memory.

Ratio (member) and Ratio (node)The LTM system distributes connections among machines according to ratio weights that you define, where the number of connections that each machine receives over time is proportionate to a ratio weight you define for each machine. These are static load balancing methods, basing distribution on static user-assigned ratio weights that are proportional to the capacity of the servers. Regarding Ratio load balancing:

Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation). This distinction is especially important with the Ratio method; with the Ratio (member) method, the actual ratio weight is a member setting in the pool definition, whereas with the Ratio (node) method, the ratio weight is a setting of the node.

The default ratio setting for any node is 1. If you use the Ratio (as opposed to Ratio (member) load balancing method, you must set a ratio other than 1 for at least one node in the configuration. If you do not change at least one ratio setting, the load balancing method has the same effect as the Round Robin load balancing method.

Warning: If you set the load balancing method to Ratio (node), as opposed to Ratio (Member), you must define a ratio setting for each node.

Dynamic RatioThe Dynamic Ratio method is like the Ratio method except that ratio weights are based on continuous monitoring of the servers and are therefore continually changing.

This is a dynamic load balancing method, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

The Dynamic Ratio method is used specifically for load balancing traffic to RealNetworks® RealSystem® Server platforms, Windows® platforms equipped with Windows Management Instrumentation (WMI), or any server equipped with an SNMP agent such as the UC Davis SNMP agent or Windows 2000 Server SNMP agent. To implement Dynamic Ratio load balancing, you must first install and configure the necessary server software for these systems, and then install the appropriate performance monitor. For more information, see Appendix A, Additional Monitor Considerations.

Fastest (node) and Fastest (application)The Fastest methods pass a new connection based on the fastest response of all currently active nodes. These methods may be particularly useful in environments where nodes are distributed across different logical networks. Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

Least Connections (member) and Least Connections (node)The Least Connections methods are relatively simple in that the LTM system passes a new connection to the node that has the least number of current connections. Least Connections methods work best in environments where the servers or other equipment you are load balancing have similar capabilities.

These are dynamic load balancing methods, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

Observed (member) and Observed (node)The Observed methods use a combination of the logic used in the Least Connections and Fastest modes. With the Observed methods, nodes are ranked based on a combination of the number of current connections and the response time. Nodes that have a better balance of fewest connections and fastest response time receive a greater proportion of the connections. The Observed modes also work well in any environment, but may be particularly useful in environments where node performance varies significantly.

These are dynamic load balancing methods, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

Predictive (member) and Predictive (node)The Predictive methods also use the ranking methods used by the Observed methods, where nodes are rated according to a combination of the number of current connections and the response time. However, with the Predictive methods, the LTM system analyzes the trend of the ranking over time, determining whether a node's performance is currently improving or declining. The nodes with better performance rankings that are currently improving, rather than declining, receive a higher proportion of the connections. The Predictive methods work well in any environment.

The Predictive methods are dynamic load balancing methods, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

Specifying priority-based member activation

You can load balance traffic across all members of a pool or across only members that are currently activated according to their priority number. In priority-based member activation, each member in a pool is assigned a priority number that places it in a priority group designated by that number.

With all pool members available (meaning they are enabled, marked up, and have not exceeded their connection limit), the LTM system distributes connections to all members in the highest priority group only, that is, the group designated by the highest priority number. The Priority Group Activation value determines the minimum number of members that must remain available for traffic to be confined to that group. If the number of available members in the highest priority group drops below the minimum number, the LTM system also distributes traffic to the next higher priority group, and so on.

The configuration shown in Figure 4.1 has three priority groups, 3, 2, and 1. Connections are first distributed to all pool members with priority 3 (the highest priority group). If fewer than two priority 3 members are available, traffic is directed to the priority 2 members as well. If both the priority 3 group and the priority 2 group have fewer than two members available, traffic is directed to the priority 1 group. The LTM system continuously monitors the higher priority groups, and each time a higher priority group once again has the minimum number of available members, the LTM system again limits traffic to that group.

Specifying pool members

When you configure this setting, you are specifying the servers (that is, pool members) that will make up the load balancing pool. To specify a pool member, you must specify the server's IP address, and a service port. An optional setting is the ratio weight, applicable when you have selected the load balancing method Ratio (member), Ratio (node), or Dynamic Ratio.

Configuring pool member settings

When adding members to a pool, you can configure a number of settings for that pool member. You configure most of these settings after you have created the load balancing pool. The only settings that you must specify during pool creation are the Address and Service Port settings. All other settings have default values that you can either retain or adjust later, depending on your needs.

Before adding pool members, it is helpful to have a description of certain pool member settings that you might want to change.

Specifying an address

When you add a member to a pool, you use the Address setting to specify the IP address of that pool member. You can do this either by typing an IP address or by selecting an IP address from the node list. This setting is required.

Specifying a service port

The Service Port setting represents either the service name or the port number for the service associated with the pool member. This setting is required.

Specifying a ratio weight for a pool member

When using a ratio-based load balancing method for distributing traffic to servers within a pool, you can use the Ratio setting to assign a ratio weight to the server. The ratio weight determines the amount of traffic that the server receives.

Specifying priority-based member activation

The Priority setting assigns a priority number to the pool member. Within the pool, traffic is then load balanced according to the priority number assigned to the pool member. Thus, members that are assigned a high priority receive the traffic until the load reaches a certain level, at which time the traffic goes to members assigned to the next lower priority group.

You configure the load level that determines when the LTM system begins directing traffic to members of a lower priority through the pool setting Priority Group Activation. For more information, see Specifying priority-based member activation.

Specifying a connection limit

With the Connection Limit setting, you can specify the maximum number of concurrent connections allowed for a pool member. Note that the default value of 0 (zero) means that there is no limit to the number of concurrent connections that the pool member can receive.

Selecting an explicit monitor association

Once you have associated a monitor with a pool, the LTM system automatically associates that monitor with every pool member, including those members that you add to the pool later. However, in some cases you might want the monitor for a specific pool member to be different from that assigned to the pool. In this case, you must use the Health Monitors setting to specify that you want to explicitly associate a specific monitor with the pool member.

You can also configure this setting to prevent the LTM system from associating any monitor with that pool member.

To explicitly associate a monitor with a pool member, locate the Health Monitors setting and select Member Specific, which causes the Select Monitors setting to appear. Then configure the Select Monitors setting as described in the following section.

To ensure that the LTM system associates no monitor with the pool member, set the Health Monitors setting to None.

Creating an explicit monitor association for a pool member

The LTM system contains many different monitors that you can associate with a pool member, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with pool members. The only monitor types that are not available for associating with pool members are monitors that are specifically designed to monitor nodes and not pools or pool members. These monitor types are:

To associate a monitor with an individual pool member, you simply display the pool member settings and set the Health Monitors setting to Member Specific. This displays the Select Monitors setting. Select the monitor that you want to associate with the pool member, and using the left arrows (<<), move the monitor name to the Active box. Clicking Finished or Update activates the monitor association for that pool member only.

Associating multiple monitors with the same pool member

The LTM system allows you to associate more than one monitor with the same server. Using the Configuration utility, you can:

Associate more than one monitor with a member of a single pool.For example, you can create monitors http1, http2, and http3, where each monitor is configured differently, and associate all three monitors with the same pool member. In this case, the pool member is marked as down if any of the checks are unsuccessful.

Assign one IP address and service to be a member of multiple pools.Then, within each pool, you can associate a different monitor with that pool member. For example, suppose you assign the server 10.10.10:80 to three separate pools: my_pool1, my_pool2, and my_pool3. You can then associate all three custom HTTP monitors to that same server (one monitor per pool). The result is that the LTM system uses the http1 monitor to check the health of server 10.10.10.:80 in pool my_pool1, the http2 monitor to check the health of server 10.10.10.:80 in pool my_pool2, and the http3 monitor to check the health of server 10.10.10:80 in pool my_pool3.

You can make multiple-monitor associations either at the time you add the pool member to each pool, or by later modifying a pool member's properties.

Managing pools and pool members

When generally managing pools and pool members, you typically need to view existing pool or pool member configurations. Occasionally, you might need to perform other management tasks as well. Using the Configuration utility, you can:

To display pool member properties

In the Members column, click the number shown.This lists the members of that pool.

In the Current Members list, click a pool member address.This displays the properties for that pool member.

Removing monitor associations

You can remove any existing monitor associations for a pool or pool member.

To remove a monitor from a pool, access the properties page for the pool and change the Health Monitors setting by moving the monitor name in the Active box to the Available box.

To remove an explicit monitor association on an individual pool member, access the properties page for the pool member and change the Health Monitors setting to either Inherit from Pool or None. Selecting None excludes the pool member from any monitoring that you have configured on that pool.

Deleting a pool

To delete an existing pool, use the following procedure. For information on removing individual pool members from a pool, see Modifying existing pool members.

Before deleting a pool, you must first remove the pool as a resource from the virtual server.

To delete a pool

On the Main tab, expand Local Traffic.

Click Pools.This displays a list of existing pools.

In the left column next to a pool name, check the Select box.

Click Delete.This displays the Delete Confirmation screen.

Click Delete.

Viewing pool and pool member statistics

Using the Configuration utility, you can view statistics related to existing pools and pool members.

To view pool and pool member statistics, display the list of existing pools or the list of existing pool members. Then click Statistics on the menu bar. This opens the Statistics screen, which shows statistics for all existing pools and their pool members.